'Habitat has been improved by the active management of browsers and predators and it's still improving,' he added.

Mainly confined to broadleaf forests of southern Chatham Island, parea are surveyed every five years to gauge the success of management, said a DoC release.

The surveys are undertaken during the breeding season, when the birds sit in prominent locations and undertake dramatic, and highly visible, display flights. The scientists sit on hilltop vantage points to count them and estimate the number of breeding territories.

'We were ecstatic when we returned to survey the birds last week to find such a huge increase in their population,' said Adams.